In shears for removing wool from sheep, it has been conventional to utilize a mechanically operated clipper head which is driven by an extended rotating shaft which is powered by a remote electric motor. Such a unit features a lightweight clipper head which dissipates a minimal amount of thermal energy, a feature which is highly desirable from the standpoint of an operator's convenience and comfort. Furthermore, the conventional clipper head produces relatively little noise which might frighten an animal and thereby cause injury to the animal or damage to its fleece. Thus, while shears having a self-contained electric motor are also known, the more favorable heat, weight and noise characteristics of the remote motor design have established it as the dominant design for commercial sheep shearing equipment in the United States and abroad.
One type of remote motor shearing machine which has heretofore been used is one in which a rigid rotating shaft connects the clipper head to the remote motor. In order to impart sufficient angular and translational mobility to the clipper head, so that it may easily reach all portions of the animal to be sheared, one or more knuckle joints are interposed in the rigid shaft. Hinges in these joints permit shaft movement, while the knuckles transmit the rotational motion of each shaft element through the joint toward the clipper head.
The combination jointed shaft and remote motor shearer, despite widespread use, is subject to a number of shortcomings. Increasing the maneuverability of the shaft, as required for maximum ease of shearing, can be accomplished only by increasing the number of knuckle joints in the shaft, which in turn increases the difficulty of maintaining the shaft in proper position during shearing. Further, the exposed gears which rotate in each knuckle joint present a significant safety hazard to persons or animals that may be caught and injured in the gears. Elimination of this hazard, by shielding the gears in each joint, can be accomplished only at the cost of restraining the flexibility of each joint and thus reducing the manueverability of the apparatus. A further safety problem associated with the rigid shaft shears arises when the blades of the clipper head are stopped by a heavy shearing load and the shaft is thereby caused to twist or swing by the excess torque developed by the motor. Such a moving shaft presents a significant hazard to persons and animals in the work area, primarily because of the danger of being struck by one of the shaft's relatively heavy knuckle joints. In view of these problems, and in light of the trend of increasingly strict governmental safety regulations for the workplace, it is possible that a safer substitute will be required for the rigid jointed shaft/remote motor shearing machine at some point in the future.
Replacement of the rigid jointed shaft by a flexible shaft in a remote motor shearing unit eliminates many of the above-described disadvantages. A flexible shaft offers substantially unrestricted mobility for the clipper head of the shears unit, while offering greater safety as well, because the flexible shaft carries no exposed gears or heavy joints which may injure persons or animals in the shearing area. Because a flexible shaft unit also lacks much of the expensive gearing of its rigid jointed shaft counterpart, it may be produced and maintained at a lower cost as well. Examples of flexible shaft shearing apparatus include Great Britain Pat. No. 906 of 1908, issued to Bousfield; Great Britain Pat. No. 466,292, issued to Macnamara, et al.; U.S. Pat. No. 973,696, issued to Ponath; and U.S. Pat. No. 2,662,412, issued to Miller.
Notwithstanding its advantages over the rigid jointed shaft, the flexible shaft shearing machines of the prior art have found little acceptance in commercial sheep shearing in the United States, and, as far as is known, only a limited acceptance abroad. The reason for this lack of acceptance rests in the behavior of prior art flexible shaft apparatus when the clipper head encounters a heavy shearing load. When this occurs, the torque produced by the motor cannot be transmitted in whole to the clipper head because the load on the clipper head prevents full-speed action by the clipper blades of the clipper head. Torque transmission through the flexible shaft is further hindered by bending of the shaft, which obstructs its turning motion. In this situation, which may occur frequently with the shaft characteristics of prior art devices, excess motor torque will be transmitted to the shaft itself, and to its housing, thereby causing the shaft to twist around itself.
When twisting of the shaft occurs, transmission of power to the clipper head is stopped and shearing must be discontinued until the operator can shut off the motor and thereafter untwist the flexible shaft. Since the operator of present day sheep shearing equipment generally holds the animal while the shears are operated, the operator must ordinarily release the animal before untwisting the shaft and must thereafter recapture and reorient the animal to the appropriate position before shearing may resume. Such a process is not only time consuming in itself, but also threatens to frighten the animal and thereby increase its resistance to further shearing, which may result in further delays or in possible injury to the animal. Further, interruption of the shearing may render it impossible to remove the animal's fleece in a single piece, or may require the making of second cuts to complete the shearing. Either of these eventualities is likely to reduce the quality and value of the wool ultimately obtained.
Because of the difficulties associated with twisting cable, prior art flexible shaft shearing apparatus have generally been suitable only for relatively very light shearing loads which do not cause the motor to develop sufficient excess torque to cause twisting of the shaft. For example, in Australia and New Zealand, flexible shaft/remote motor shears have found a limited use for "tagging", a process in which relatively short strokes are used to remove wool from the udder and tail areas of ewes prior to lambing. However, conventional rigid shaft equipment continues to be used in these countries for heavier shearing.